If you are writing prose a . (full stop) is there to show a the end of a sentence so that you know when the next one starts. If you only have one sentence, then it isn't strictly necessary for clarity. Hence, if it's a short notification message of only one sentence, you can leave it out.
That said you should keep to the style guides given for your mobile platform. Android for example includes them in the examples in their Design Guide.
I recommend keeping the . unless you have a good reason to leave it out.